1. Field of the Invention
The present invention relates to optical aberration measurement and correction, and, more particularly, to a system and method for achieving an empirical, global optimization of an objective measurement and correction of an optical system such as the human eye.
2. Description of Related Art
Optical systems having a real image focus can receive collimated light and focus it at a point. Such optical systems can be found in nature, e.g., human and animal eyes, or can be manmade, e.g., laboratory systems, guidance systems, and the like. In either case, aberrations in the optical system can affect the system's performance.
A perfect or ideal human eye diffusely reflects an impinging light beam from its retina through optics of the eye, which includes a lens and a cornea. For such an ideal eye in a relaxed state, i.e., not accommodating to provide near-field focus, reflected light exits the eye as a sequence of plane waves. However, a real eye typically has aberrations that cause deformation or distortion of reflected light waves exiting the eye. An aberrated eye diffusely reflects an impinging light beam from its retina through its lens and cornea as a sequence of distorted wavefronts.
It is known in the art to perform laser correction of focusing deficiencies by photorefractive keratectomy (PRK), which modifies corneal curvature, and LASIK surgery. Such methods typically employ a 193-nm excimer laser to ablate corneal tissue. Munnerlyn et al. (J. Cataract Refract. Surg. 14(1), 46–52, 1988) have presented equations for determining a specific volume of tissue to be removed to achieve a desired refractive correction. Frey (U.S. Pat. No. 5,849,006) teaches a method of using a small-spot laser to remove a desired volume of tissue for effecting a desired refractive correction.
In U.S. application Ser. No. 09/566,668, filed May 8, 2000, for “Apparatus and Method for Objective Measurement and Correction of Optical Systems Using Wavefront Analysis,” commonly owned with the present application, the disclosure of which is incorporated herein by reference, it is taught to use Zernike polynomials to approximate a distorted wavefront emanating from an aberrated eye. In this approach a wavefront W(x,y) is expressed as a weighted sum of individual polynomials, with i running from 0 to n, of CiZi(x,y), where the Ci are the weighting coefficients and the Zi(x,y) are the Zernike polynomials up to some order. As illustrated in FIG. 8A, a pre-operatively measured wavefront 70 is treated with an algorithm 71 to form a treatment profile 72, which is then transmitted to a corneal ablation system for treating the aberrated eye.